Octupole correlation between the multiple chiral doublet bands

Octupole correlation between the multiple chiral doublet bands in 78 Br Speaker: S. Y. Wang (王守宇) Shandong University, Weihai，China

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Contents 1 Introduction 2 Experimental Details 3 Result and Discussions 4 Conclusion 5 Acknowledgement

Contents 1 Introduction 2 Experimental Details 3 Result and Discussions 4 5 Conclusion Acknowledgements

Chirality exists commonly in nature Left- ØChiral symmetry is a well-known phenomenon in chemistry, biology and particle physics. Right-

Introduction “chiral rotation” Left-handed Right-handed ØIn 1997, Frauendorf and Meng pointed out that the rotation of triaxial nuclei may attain a chiral character. ØThe angular momentum of the valence proton, valence neutron, and the rotation core in the triaxial nuclei may form either a left- or right- system. Frauendorf and Meng NPA 617, 131 (1997)

Introduction Intrinsic frame Frauendorf and Meng NPA 617, 131(1997) chiral symmetry breaking Lab. frame: restoration of symmetry breaking When the chiral symmetry is broken in the body-fixed frame, the restoration of the symmetry in the lab frame results in two nearly degenerate ΔI=1 bands, namely chiral doublet bands. Expected exp. signal： Two near degenerate DI =1 bands, called chiral doublet bands

observation of chiral bands ØSince the chirality in nuclear physics was suggested, lots of experimental studies have been devoted to search for nuclear chirality. ØIn 2001, chiral doublet bands were observed in the N = 75 isotones in the A~130 mass region.

Island of chiral rotation Later, an island of chiral rotation was found in the 130 mass region.

The observation of “chiral island” ØSo far, candidates for chiral doublet bands have been observed experimentally in about 39 cases of odd-odd, odd-A and even-even nuclei, including the 80, 100, 130, 190 mass regions. ØMost studies on nuclear chirality have focused on the 100 and 130 mass regions at first. However, there is no reason to consider the nuclei in 100 and 130 mass regions as unique in terms of the nuclear chirality. A~130 mass region: Starosta 01 etc. A~100 mass region： Vaman 04 etc.

The newly “chiral island” ØThus, it is necessary to search for more candidates in other mass regions to show that the chiral symmetry is of a general nature. ØRecently, chiral doublet bands were also reported in the 190 and 80 mass regions. A~190 mass region： Lawrie 08； Masiteng 13 A~130 mass region: Starosta 01 etc. A~100 mass region： Vaman 04 etc. A~80 mass region： 80 Br, Wang 11

multiple chiral bands (MχD) Ø In 2006, based on the triaxial RMF theory, Meng et al. , suggested that besides one pair of chiral doublet bands, multiple chiral doublet bands (MχD) could exist in one single nucleus. Ø The experimental evidences for multiple chiral doublet bands were reported in 133 Ce, 103 Rh, and possibly in 107 Ag.

Chirality in 80 mass region Ø Recently, our work on 80 Br reported a pair of bands based on the g 9/2 configuration, which provided the first evidence for chirality in the A~80 mass region.

Chirality in 80 mass region ？ Ø For this mass region, total Routhian surfaces (TRS) calculations suggest that 78 Br has a remarkable triaxial shape with γ=21. 3°and β 2=0. 32 for the rotational band based on the g 9/2− 1 configuration. Ø The deformation parameters together with the particle-hole configuration are suitable for the construction of chiral doublet bands. Landulzfo 96

Introduction ？ Ø Thus, it is interesting to populate high-spin states of 78 Br and to search for chiral doublet bands. Ø It is also important to verify whether chirality exists in more than one odd-odd nuclei in the A~80 mass region in order to provide systemic survey on the chiral interpretation.

Introduction ？ Ø It is also important to present new data on high-spin states of 78 Br and to search for the possible multiple chiral doublet bands in the A ~80 mass region.

Introduction For the odd-odd nucleus 78 Br with Z = 35 and N = 43, both proton and neutron Fermi surfaces lie near the g 9/2, f 5/2 and p 3/2 orbits. Z = 35 N = 43

Introduction Ø The g 9/2 and p 3/2 orbits have opposite parity and Δj = Δl = 3 ħ, the interaction between these orbits will lead to the octupole correlation effect. Ø Therefore, octupole correlation effect is also expected in 78 Br, which would provide an unique chance to study the octupole correlation effect in the chiral nucleus. Ø Based on the above considerations, experiments were performed to study high-spin states of the odd-odd nucleus 78 Br. Butler 96

Contents 1 Introduction 2 Experimental Details 3 Result and Discussions 4 Conclusion 5 Acknowledgements

Experimental Details Ø Our experiment was carried out at the i. Themba LABS in South Africa.

Experimental Details The 70 Zn (12 C, 1 p 3 n) reaction is used to populate the high-spin states of 78 Br at beam energies of 60&65 Me. V. Cross sections have been calculated with the PACE 2 program.

Experimental Details Ø The Zn target is the self-supported metallic foil with a thickness of 0. 85 mg/cm 2.

Experimental Details Ø The γ-rays were recorded by the detector array AFRODITE, which consists of 8 Compton Suppressed Clover detectors. Ø Four clovers are placed at 135°with respect to the beam direction, while other four are placed at 90°. Ø Thus, we may extract the ADO ratios of gamma-rays to obtain information on the multipolarities.

Experimental Details Ø The particle detectors array DIAMANT was also used to select reaction channels. Ø A total of 1500 million γ-γ coincidence events were recorded in the experiment. Ø 160 million p-γ-γ coincidence events are picked out by the DIAMANT array.

Contents 1 Introduction 2 Experiments 3 Result and Discussions 4 Conclusion 5 Acknowledgements

The previous studies ØPrior to the present work, the ground state of 78 Br had been assigned I = 1+ with the p 3/2 p 1/2 configuration. ØThree isomeric states (2− at 32. 3 ke. V, 4+ at 180. 9 ke. V, and 5(+) at 227. 7 ke. V) had been reported in the previous studies. Isomer T 1/2 configuration 1+ 6. 5 min πp 3/2 υp 1/2 2 - 14. 2 ns πp 3/2 υg 9/2 4+ 119. 2 μs πg 9/2 υg 9/2 5(+) 84 ns unknown ØThe measured g-factors indicated that the 2− and 4+ isomeric states came from the p 3/2 g 9/2 and g 9/2 configurations, respectively. Demuynck 70, Christiansen 72, Pleiter 73, Bermudez 80

The previous studies ØHigh-spin states of 78 Br have also been studied by in-beam gamma measurements. ØTwo rotational bands were also reported in 78 Br. The positive-parity band has been assigned the πg 9/2 νg 9/2 configuration, while no configuration assignment for the negative-parity band was given in the previous works. Behar 82, Landulfo 96

The present level scheme ØLevel scheme for 78 Br obtained in this work. ØNew observed transitions are shown by red lines.

The present level scheme ØA total of 46 new transitions and 25 new levels have been added into the level scheme. ØFive rotational bands are observed in the present work and labeled as 1 -5 for the convenience of discussions.

The present level scheme ØThe present work confirms most of the previously known level structures, and extends bands 1 and 3 up to 20+ and 19−, respectively. Ø Furthermore, 15 new interband transitions and three new rotational bands labeled as 2, 4, and 5 have been identified and added in the present level scheme.

The present level scheme preliminary ØThis figure shows the sample spectra supporting the present level scheme. ØMost of new gamma-rays can be clearly seen in this figure.

Results and Discussion ØOne of the interesting aspects of the present work is the observation of two pairs of nearly degenerate bands.

Results and Discussion ØOne of the interesting aspects of the present work is the observation of two pairs of nearly degenerate bands. Bands 1 and 2 Bands 3 and 4

Bands 1 and 2 In order to discuss the features of the two pairs of nearly degenerate bands, the experimental energy E(I), energy staggering parameter S(I), and B(M 1)/B(E 2) ratios are extracted and shown in this figure. Ø bands 1 and 2 maintain a small energy difference. Ø They have similar S(I) and B(M 1)/B(E 2) values within the observed spin region. Ø The B(M 1)/B(E 2) values show obvious oddeven stagger. Ø The two positive parity bands in 78 Br show similar experimental features with those in 80 Br, which have been suggested as the first candidate of chiral bands in the 80 mass region. Taking the experimental results into account, bands 1 and 2 in 78 Br may be considered as a candidate for chiral doublet bands.

Bands 3 and 4 Ø For band 3, no configuration assignment was given in the previous studies. Ø Bands 3 and 4 show similar experimental features. Ø The presence of strong linking transitions points to both bands having the same configurations. Ø Thus, we suggest bands 3 and 4 as another candidate for chiral doublet bands in 78 Br.

Configurations of bands 3 and 4? Among the single-particle orbits which lie close to the Fermi level, the p 3/2 or f 5/2 and g 9/2 orbits occupied by the unpaired proton or neutron will lead to the negative parity. Z = 35 N = 43

Configurations of bands 3 and 4? Isomer T 1/2 configuration 1+ 6. 5 min πp 3/2 υp 1/2 2 - 14. 2 ns πp 3/2 υg 9/2 4+ 119. 2 μs πg 9/2 υg 9/2 5(+) 84 ns unknown We tentatively assigned the πf 5/2 νg 9/2 configuration for bands 3 and 4, because the πp 3/2 νg 9/2 configuration has been assigned to the 2− isomer of 78 Br. g 9/2 f 5/2 g 9/2

theoretical calculations In order to discuss the features of the two pairs of nearly degenerate bands, theoretical calculations based on a combination of the multidimensional constrained relativistic mean-field (MDCRMF) approach and the triaxial particle-rotor model (TPRM) were performed.

MDC-RMF Calculations Based on the multidimensional constrained relativistic mean-field (MDC-RMF) calculations, the deformation parameters are (β 2, γ) = (0. 32, 15. 1 ) and (0. 23, 26. 3 ) for the two pairs of bands, respectively. For the isomers and the bandheads of bands 1 and 3, the calculated energies relative to the ground state are coincident with the corresponding experimental data. The deformation parameters of the calculated states in 78 Br are listed in this table. Lu 12, Zhao 12, Lu 14

Triaxial particle-rotor model (TPRM) calculation These deformation parameters from the (MDC-RMF) calculations are adopted as inputs in the TPRM calculations. The other input parameters are obtained as follows: Wang 07, Zhang 07, Wang 08

Triaxial particle-rotor model (TPRM) calculation The calculated results for bands 1, 2 and bands 3, 4 in 78 Br were shown in this Figure, together with the corresponding experimental results. Ø The theoretical results show a good agreement with the experimental data. Ø For the two pairs of bands, the magnitude, stagger, and trend of the E(I), S(I) and the B(M 1)/B(E 2) ratios are reproduced quite well. Ø The good agreement between the calculated values and the available experimental data supports the present configuration assignments.

The effective angles • To obtain a clear chiral pictures of 78 Br, the effective angles between the angular momentum of the valence proton, valence neutron, and rotation core for the two pairs of doublet bands in the body-fixed frame are calculated by the TPRM as follows in Ref{Wang 08} and shown in this figure.

The effective angles ØFor bands 1 and 2, the effective angles are larger than 45◦ in the observed spin region. ØFor bands 3 and 4, the effective angles are larger than 45◦ in the low spin region, while the effective angle between the rotation core and the valence neutron are close to 45◦ in the high spin region. Ø The calculated results suggest the clear nonplanar（aplanar） rotations for bands 1, 2 and bands 3, 4 in 78 Br. Ø Based on the above analysis, bands 1, 2 and bands 3, 4 in 78 Br can be interpreted as two pairs of chiral doublet bands, thereby forming a multiple chiral doublet bands (MχD).

Results and Discussion In short, the observed two positive-parity bands and two negative-parity bands are proposed to be multiple chiral doublet bands with the πg 9/2 νg 9/2 and πf 5/2 νg 9/2 configurations, respectively.

Results and Discussion Another interesting aspect of the present work is the observation of the five new linking transitions between the opposite-parity bands 1 and 3.

Results and Discussion The observation of the E 1 transitions between bands 1 and 3 indicates that octupole correlations exist in 78 Br.

Results and Discussion g 9/2 ØThe observation of octupole correlation effect indicates there is a p 3/2 component mixed with the f 5/2 component as the two orbits are very close to each other in energy. ØThe interaction between the g 9/2 and the p 3/2 components in the configurations will give rise to the octupole correlations effect in 78 Br. f 5/2 g 9/2

Results and Discussion The MDC-RMF is also used to calculate the octupole deformation of contour separation is 0. 2 Me. V. 78 Br. The calculated potential energy surface for the ground state of 78 Br in the β 20 -β 30 plane is given in this figure. Ø The potential energy surface is very soft with respect to the β 30 degree of freedom, which implies the possibility of octupole correlations. Ø The observation of octupole correlation effect in 78 Br indicates that chiral geometry can exist in octupole soft nuclei.

Results and Discussion To study the octupole correlation effect, the experimental B(E 1)/B(E 2) ratios as a function of spin are extracted and shown in this figure. The experimental B(E 1)/B(E 2) ratios as a function of spin in 78 Br. We can see clearly from the figure that the experimental B(E 1)/B(E 2) ratios increase with the spin increases, which indicates that octupole correlation effect becomes more remarkable as the spin increases.

Results and Discussion ØWe note that the octupole correlation effect becomes stronger as the spin increases. ØHowever, the absence of the side bands at high spin region for two pairs of chiral bands means the chiral effect becomes weaker or even vanishes. A competition between octupole correlation effect and chirality is clearly shown in 78 Br.

Contents 1 Introduction 2 Experiments 3 Result and Discussions 4 Conclusion 5 Acknowledgements

Conclusion Ø High-spin states of 78 Br were populated using the 70 Zn(12 C, 1 p 3 n) reaction at the i. Themba LABS in South Africa. Ø The previously known level scheme of 78 Br has been extended. The observed two positive-parity bands and two negative-parity bands are proposed to be multiple chiral doublet bands. Ø The octupole correlation effect is also observed in 78 Br. Ø It is the first identification of octupole correlation between multiple chiral doublet bands in atomic nuclei. The observation indicates that chiral geometry can exist in octupole soft nuclei. A competition between octupole correlation effect and chirality is clearly shown in 78 Br.

Acknowledgement i. Themba Labs: R. Bark, E. Lawrie, T. D. Bucher, A. Kamblawe, E. Khaleel, N. Khumalo, E. A. Lawrie, J. J. Lawrie, P. Jones, S. M. Mullins, S. Murray, M. Wiedeking, S. N. T. Majola, J. Ndayishimye, D. Negi, S. P. Noncolela, O. Shirinda, P. Sithole, M. A. Stankiewicz, T. Dinoko, J. Easton Stellenbosch University: S. M. Wyngaardt, P. Papka, University of the Western Cape: J. F. Sharpey-Schafer, J. N. Orce University of Zululand: S. S. Ntshangase ATOMKI, Hungury: B. M. Nyakó, K. Juhász Peking Univ. : J. Meng, S. Q. Zhang, H. Hui, X. Q. Li, C. Xu, Tsinghua Univ: Z. G. Xiao, H. J. Li Shandong Univ: B. Qi, C. Liu, Thank you for your attention and suffer from my spoken English. Supported by NSFC & NRF & China-SA collaboration!